1. Field of the Invention
The present invention relates to a developing device for visualizing an electrostatic latent image in an electrophotographic apparatus or electrostatic recording apparatus.
2. Description of the Related Art
Electrophotography, electrostatic recording, and other image forming systems are applied to modern image forming apparatuses. Among these systems is a prevailing developing system for visualizing an electrostatic latent image. This system is based on the two-component developing method in which the latent image is electrostatically developed by means of a developing agent, a mixture of a toner as a coloring material and a carrier as a magnetic material.
The two-component developing method, however, is subject to a drawback such that it requires control of the mixture ratio between the toner and the carrier, as well as use of a large-sized complicated developing device. Therefore, some of modern small-sized copying machines and printers use the one-component developing method which requires no carrier. In particular, the nonmagnetic one-component developing method, in which no magnets are arranged in the developing device, has some advantages, such as the reduction of the size and weight of the developing device, low cost, ease of conversion to color developing, etc. Many research reports recently been made on this method.
In a conventional developing device of this type, the toner (developing .agent) stored in a hopper is delivered to a developing roller by means of a toner supply roller, which is in contact with the developing roller and rotatable in the same direction therewith. Subsequently, a thin layer of the toner is formed on the developing roller by means of a thin layer forming member, which is in linear contact with the developing roller under uniform pressure, and the toner layer is brought close to or into contact with an image carrier. By doing this, an electrostatic latent image on the image carrier is visualized.
In reproducing a continuous image, such as an entirely solid black image, which requires high density throughout a wide area, by means of the conventional developing device described above, however, the toner supply to the developing roller cannot cover the toner consumption, so that the thin toner layer cannot be formed satisfactorily. Thus, there has been a fatal problem on the quality of a solid image, lower density at the trailing end portion of the image compared with the leading end portion thereof.